Abstract
The Standard Model Effective Field Theory (SMEFT) offers a powerful theoretical framework for parameterizing the low-energy effects of heavy new particles with masses far above the scale of electroweak symmetry breaking. Additional light degrees of freedom extend the effective theory. We show that light new particles that are weakly coupled to the SM via non-renormalizable interactions induce non-zero Wilson coefficients in the SMEFT Lagrangian via renormalization-group evolution. For the well-motivated example of axions and axion-like particles (ALPs) interacting with the SM via classically shift-invariant dimension-5 interactions, we calculate how these interactions contribute to the one-loop renormalization of the dimension-6 SMEFT operators, and how this running sources additional contributions to the Wilson coefficients on top of those expected from heavy new states. As an application, we study the ALP contributions to the magnetic dipole moment of the top quark and comment on implications of electroweak precision constraints on ALP couplings.
Highlights
On the other hand, there remains the possibility of the existence of light new particles interacting very weakly with the SM, for instance because these interactions are mediated by higher-dimensional operators
For the well-motivated example of axions and axion-like particles (ALPs) interacting with the SM via classically shift-invariant dimension-5 interactions, we calculate how these interactions contribute to the one-loop renormalization of the dimension-6 Standard Model Effective Field Theory (SMEFT) operators, and how this running sources additional contributions to the Wilson coefficients on top of those expected from heavy new states
Many of the dimension-6 operators which receive contributions from ALP-induced RG evolution effects are strongly constrained, for example by measurements of electroweak precision observables and of the properties of the Higgs boson, the top quark and the gauge bosons at the LHC. This implies that areas of the ALP parameter space which may still be unconstrained by direct searches can be probed indirectly, using constraints on dimension-6 SMEFT operators implied by precision studies
Summary
An ALP provides a paradigmatic example of a new light particle, which interacts weakly with the SM via effective interactions suppressed by a large scale f ma. It is well known that the derivative ALP couplings to fermions are only defined modulo the generators of exact global symmetries of the SM [50], which are baryon number B and the lepton numbers Le, Lμ and Lτ for each flavor (since the neutrinos are massless in the SM) It follows that four model parameters are redundant and can be chosen at will. These rules imply, in particular, that the ALP-boson couplings cV V should be accompanied by a loop factor [21] This is natural in QCD axion models, because the θ parameter, which is dynamically set to zero by a shift of the axion field in the Peccei-. In this paper we present a systematic study of these effects at one-loop order
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